- Value root_search(Position& pos, SearchStack* ss, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
-
- EvalInfo ei;
- StateInfo st;
- CheckInfo ci(pos);
- int64_t nodes;
- Move move;
- Depth depth, ext, newDepth;
- Value value, alpha, beta;
- bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
- int researchCountFH, researchCountFL;
-
- researchCountFH = researchCountFL = 0;
- alpha = *alphaPtr;
- beta = *betaPtr;
- isCheck = pos.is_check();
-
- // Step 1. Initialize node and poll (omitted at root, init_ss_array() has already initialized root node)
- // Step 2. Check for aborted search (omitted at root)
- // Step 3. Mate distance pruning (omitted at root)
- // Step 4. Transposition table lookup (omitted at root)
-
- // Step 5. Evaluate the position statically
- // At root we do this only to get reference value for child nodes
- if (!isCheck)
- ss->eval = evaluate(pos, ei, 0);
-
- // Step 6. Razoring (omitted at root)
- // Step 7. Static null move pruning (omitted at root)
- // Step 8. Null move search with verification search (omitted at root)
- // Step 9. Internal iterative deepening (omitted at root)
-
- // Step extra. Fail low loop
- // We start with small aspiration window and in case of fail low, we research
- // with bigger window until we are not failing low anymore.
- while (1)
- {
- // Sort the moves before to (re)search
- rml.sort();
-
- // Step 10. Loop through all moves in the root move list
- for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
- {
- // This is used by time management
- FirstRootMove = (i == 0);
-
- // Save the current node count before the move is searched
- nodes = TM.nodes_searched();
-
- // Reset beta cut-off counters
- TM.resetBetaCounters();
-
- // Pick the next root move, and print the move and the move number to
- // the standard output.
- move = ss->currentMove = rml.get_move(i);
-
- if (current_search_time() >= 1000)
- cout << "info currmove " << move
- << " currmovenumber " << i + 1 << endl;
-
- moveIsCheck = pos.move_is_check(move);
- captureOrPromotion = pos.move_is_capture_or_promotion(move);
-
- // Step 11. Decide the new search depth
- depth = (Iteration - 2) * OnePly + InitialDepth;
- ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
- newDepth = depth + ext;
-
- // Step 12. Futility pruning (omitted at root)
-
- // Step extra. Fail high loop
- // If move fails high, we research with bigger window until we are not failing
- // high anymore.
- value = - VALUE_INFINITE;
-
- while (1)
- {
- // Step 13. Make the move
- pos.do_move(move, st, ci, moveIsCheck);
-
- // Step extra. pv search
- // We do pv search for first moves (i < MultiPV)
- // and for fail high research (value > alpha)
- if (i < MultiPV || value > alpha)
- {
- // Aspiration window is disabled in multi-pv case
- if (MultiPV > 1)
- alpha = -VALUE_INFINITE;
-
- // Full depth PV search, done on first move or after a fail high
- value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, false, 0);
- }
- else
- {
- // Step 14. Reduced search
- // if the move fails high will be re-searched at full depth
- bool doFullDepthSearch = true;
-
- if ( depth >= 3 * OnePly
- && !dangerous
- && !captureOrPromotion
- && !move_is_castle(move))
- {
- ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
- if (ss->reduction)
- {
- // Reduced depth non-pv search using alpha as upperbound
- value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, true, 0);
- doFullDepthSearch = (value > alpha);
- }
- }
-
- // Step 15. Full depth search
- if (doFullDepthSearch)
- {
- // Full depth non-pv search using alpha as upperbound
- ss->reduction = Depth(0);
- value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, true, 0);
-
- // If we are above alpha then research at same depth but as PV
- // to get a correct score or eventually a fail high above beta.
- if (value > alpha)
- value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, false, 0);
- }
- }
-
- // Step 16. Undo move
- pos.undo_move(move);
-
- // Can we exit fail high loop ?
- if (AbortSearch || value < beta)
- break;
-
- // We are failing high and going to do a research. It's important to update
- // the score before research in case we run out of time while researching.
- rml.set_move_score(i, value);
- update_pv(ss, 0);
- TT.extract_pv(pos, ss->pv, PLY_MAX);
- rml.set_move_pv(i, ss->pv);
-
- // Print information to the standard output
- print_pv_info(pos, ss, alpha, beta, value);
-
- // Prepare for a research after a fail high, each time with a wider window
- *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
- researchCountFH++;
-
- } // End of fail high loop
-
- // Finished searching the move. If AbortSearch is true, the search
- // was aborted because the user interrupted the search or because we
- // ran out of time. In this case, the return value of the search cannot
- // be trusted, and we break out of the loop without updating the best
- // move and/or PV.
- if (AbortSearch)
- break;
-
- // Remember beta-cutoff and searched nodes counts for this move. The
- // info is used to sort the root moves for the next iteration.
- int64_t our, their;
- TM.get_beta_counters(pos.side_to_move(), our, their);
- rml.set_beta_counters(i, our, their);
- rml.set_move_nodes(i, TM.nodes_searched() - nodes);
-
- assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
- assert(value < beta);
-
- // Step 17. Check for new best move
- if (value <= alpha && i >= MultiPV)
- rml.set_move_score(i, -VALUE_INFINITE);
- else
- {
- // PV move or new best move!
-
- // Update PV
- rml.set_move_score(i, value);
- update_pv(ss, 0);
- TT.extract_pv(pos, ss->pv, PLY_MAX);
- rml.set_move_pv(i, ss->pv);
-
- if (MultiPV == 1)
- {
- // We record how often the best move has been changed in each
- // iteration. This information is used for time managment: When
- // the best move changes frequently, we allocate some more time.
- if (i > 0)
- BestMoveChangesByIteration[Iteration]++;
-
- // Print information to the standard output
- print_pv_info(pos, ss, alpha, beta, value);
-
- // Raise alpha to setup proper non-pv search upper bound
- if (value > alpha)
- alpha = value;
- }
- else // MultiPV > 1
- {
- rml.sort_multipv(i);
- for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
- {
- cout << "info multipv " << j + 1
- << " score " << value_to_string(rml.get_move_score(j))
- << " depth " << (j <= i ? Iteration : Iteration - 1)
- << " time " << current_search_time()
- << " nodes " << TM.nodes_searched()
- << " nps " << nps()
- << " pv ";
-
- for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
- cout << rml.get_move_pv(j, k) << " ";
-
- cout << endl;
- }
- alpha = rml.get_move_score(Min(i, MultiPV - 1));
- }
- } // PV move or new best move
-
- assert(alpha >= *alphaPtr);
-
- AspirationFailLow = (alpha == *alphaPtr);
-
- if (AspirationFailLow && StopOnPonderhit)
- StopOnPonderhit = false;
- }
-
- // Can we exit fail low loop ?
- if (AbortSearch || !AspirationFailLow)
- break;
-
- // Prepare for a research after a fail low, each time with a wider window
- *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
- researchCountFL++;
-
- } // Fail low loop
-
- // Sort the moves before to return
- rml.sort();
-
- return alpha;
- }
-
-
- // search<>() is the main search function for both PV and non-PV nodes
-
- template <NodeType PvNode>
- Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth,
- bool allowNullmove, int threadID, Move excludedMove) {